Homopolymers of THF, also known as polytetramethylene ether glycols (PTMEG), are well known for use in spandex, polyurethanes and other elastomers. These homopolymers impart superior mechanical and dynamic properties to polyurethane elastomers, fibers and other forms of final products. As discussed in U.S. Pat. No. 4,120,903, the polymerization process of utilizing tetrahydrofuran (THF) to manufacture polytetramethylene ether glycol (PTMEG) by passing through the intermediate PTMEA (i.e., PTMEG diacetate) has been commercially practiced since about 1997. The process involves a ring-opening of THF using perfluorosulfonic acid ionomer resin as the first step in the production of the PTMEA. The most commonly known process to convert PTMEA to PTMEG is by a conventional transesterification using an alkali metal catalyst, such as sodium methylate. This method results in a residual catalyst which needs to be removed from the PTMEG product.
There are many known processes for removing the remaining alkali metal catalyst from the PTMEG product after the transesterification step. Some of these known processes are disclosed in U.S. Pat. Nos. 4,137,396, 4,985,551, 4,460,796, 4,306,943 and 6,037,381. U.S. Pat. No. 5,410,093, herein incorporated in its entirety by reference, relates to a method wherein the alkali metal catalyst is neutralized in an aqueous media in the presence of an excess amount of magnesium sulfate. The inorganic co-products of this neutralization can include sodium sulfate and magnesium hydroxide. The various inorganic solids present in PTMEG are then separated in a chamber plate filter press operation. Prior to filtration, the water must be removed from the solution containing the residual catalyst.
It is desirable to increase the filter feed rate and filter throughput between shutdowns and cleaning to improve the catalyst removal process. Moreover, maintaining the pressure drop across the filtration system is a common problem that affects both the filter feed rate and filter throughput between shutdowns. It is well known that an increased pressure drop can result in a decreased feed rate into the filtration system. This will also lead to a decreased throughput between shut down and cleaning of the filtration system.
Consequently, there is a need for a method of maintaining a desired pressure drop across the filtration system to increase the filtration feed rate and increase the throughput between shut down and cleaning of the filtration system, in a process for recovering a polyether polyol product.